Engineering topics

OKeeffe, James

Publications and source records attributed to OKeeffe, James.

3 records

NASA NTRS2003

PolyA Single Strand DNA Translocation Through an Alpha-Hemolysin Pore Stem

A new model for the polymer-pore interaction energy is introduced, based on an atomic-scale description of coulombic polymer-pore interaction. The enhanced drift velocity, experimentally observed for short polymers, is successfully accounted for, using this interaction energy model. For R/R(sub 0)>4 (R(sub 0)=7 angstroms) the translocation velocity approaches the free space drift velocity v(sub 0). This motivates the need to appropriately derivatize artificial nanopores, where R>R(sub 0).

OKeeffe, James↗

NASA NTRS2002

Local Conductance and Saturation Lengths of Atomic Wires Dipped in a Conducting Medium

We conclude that the conducting mode pi is the most likely responsible for conduction in experimental mercury-nanotube contacts. The total conductance approaches a saturation value as the dipping length is increased. There are two distinct regimes, strong and weak coupling, characterized by saturation conductances of 0 or 1G(sub o). We have calculated the partial conductance at each nanotube unit cell. The partial conductance exhibits oscillations due to reflection at the end of the tube.

OKeeffe, James↗

NASA NTRS2001

Physical and Electronic Isolation of Carbon Nanotube Conductors

Multi-walled nanotubes are proposed as a method to electrically and physically isolate nanoscale conductors from their surroundings. We use tight binding (TB) and density functional theory (DFT) to simulate the effects of an external electric field on multi-wall nanotubes. Two categories of multi-wall nanotube are investigated, those with metallic and semiconducting outer shells. In the metallic case, simulations show that the outer wall effectively screens the inner core from an applied electric field. This offers the ability to reduce crosstalk between nanotube conductors. A semiconducting outer shell is found not to perturb an electric field incident on the inner core, thereby providing physical isolation while allowing the tube to remain electrically coupled to its surroundings.

OKeeffe, James↗